Beyond the big ring: understanding gear ratios and why they matter

by Matt Wikstrom - August 11, 2014

There is more to the gearing on your bike than simply the size of your big ring. To get the most out of your gears, it serves to pay attention to the gear ratios produced by the combination of the chainrings with the rear cassette and tailoring them to suit your riding needs. In this post, CTech editor Matt Wikstrom takes a look at how to make sense of gear ratios.

Over the past decade, the number of gears on road bikes has steadily increased. Current groupsets now provide up to 22 gear combinations produced by two front chainrings and 11 rear cogs. That should be enough to contend with just about any terrain, but there is no prescription for perfect gearing. Rather, the individual must determine which gear ratios suit his or her riding style and needs.

Gear ratios

Before the advent of the chain-drive, cyclists determined that the size of the drive-wheel had a profound impact on the speeds that could be achieved. Penny-farthings were not designed with a huge front wheel for aesthetic reasons — the massive circumference allowed higher speeds provided the rider was strong enough to turn the gear.

The introduction of the chain-drive improved the efficiency of the bike because gears could be used. By combining a large cog on the cranks with a small one on the wheel, a single turn of the cranks produced multiple revolutions of the rear wheel, so it could operate just like the massive drive-wheel of a Penny-farthing.

Calculating the number of wheel revolutions produced by a bike’s gearing is simply a matter of determining the ratio of the chainring to the rear sprocket. For example, when a 53T chainring is paired with a 12T cog, it has a ratio 53:12 or 4.42 — that is, the rear wheel rotates 4.42 times for every rotation of the crank. In contrast, a 39x25T selection produces a gear ratio of 1.56.

Comparing gear ratios

A road groupset can offer a variety of gear ratios ranging from 1.21 to 4.81 in increments of 0.15-0.40. Rather than trying to understand the significance of gear ratios directly, they can be transformed into more meaningful values in one of two ways.

The first method is to relate the gear ratio to wheel size by multiplying the gear ratio by the diameter of the wheel (Figure 1A). In the case of a road wheel, 27 inches can be used for simplicity although the true diameter of a 700c rim fitted with a 23mm tyre is more like 26.3 inches. The resulting value, gear inches, is the equivalent diameter for a direct-drive wheel (like the front wheel of a Penny-farthing).

Put another way, gear inches provides the diameter of a wheel that has a circumference equivalent to the distance a geared bike will travel with one turn of the cranks and the chosen gear ratio. Thus, riding a high gear ratio such as 53x12T is equivalent to pushing a wheel with a diameter of 119 inches. In contrast, a low gear ratio like 39x25T is equivalent to a 42-inch wheel.

The second method, meters of development, is calculated by multiplying the gear ratio by the circumference of the wheel (measured in meters, Figure 1B). This value represents the distance the bike will travel with one crank revolution. Thus 53x12T yields 9.28 meters of development compared to 3.28 meters for 39x25T.

Gear inches (or meters of development) are typically presented in a gearing chart or graphed so that various combinations can be compared (Figure 2). My introduction to gear charts came with BMX racing where they proved invaluable for fine-tuning gear selection to suit the track and weather conditions. Track riders will do the same, swapping the front chainrings and/or the rear sprocket to increase or decrease the gear ratio in increments as required.

The important thing to note is that even minor differences in a ratio (e.g. 1 gear inch) influence how easily the bike can be accelerated or the maximum speed that can be attained.

Out on the road

In practice, road riders typically don’t pay much attention to gear ratios due to the abundance of choices available to them. However, there is still considerable value in fine-tuning the range of gear ratios at your disposal to maximise their utility.

I typically see riders deciding on their gearing on the basis of the largest or smallest gear ratios. Some will insist on an 11T cog, however the only time they ever use it is on a steep descent. Such thinking also fuels the debate on the merits of standard (53/39T) versus compact (50/34T) cranksets but the two offer comparable ratios. Indeed, pairing an 11-23T cassette with a compact crankset offers near-identical ratios to a standard crankset coupled with a 12-25T cassette (Figure 3).

There is a subtle difference between standard and compact cranks though. As shown in Figure 4 below, the rate at which the ratios increase is greater for standard rings than compact rings. For example, the ratios for the 11-15T cogs increase at an average rate of 7.0 gear inches/tooth for a 53T chainring compared to 6.6 gear inches/T for a 50T chainring. This difference defines the true distinction between the two cranksets by generating a different feel to the gearing at the high end.

Deciding on one over the other is difficult to do without some experience with each, but in general, the lower rate of development offered by compact cranks will suit novices and enthusiasts while racers will prefer the extra grunt offered by standard rings.

There is another consideration. Every crank and cassette combination suffers from some redundancy that reduces the number of discrete ratios on offer. A standard crankset paired with an 11-speed 11-25T cassette offers 15 discrete ratios (Figure 5A); by contrast, compact cranks paired with the same cassette afford 16 discrete ratios (Figure 5B). The difference is dictated by the combination rather than the size of the chainrings since 16 discrete ratios can be achieved by pairing an 11-28T cassette with a standard crankset (Figure 5C).

Perfect gear ratios

So what makes for perfect gearing? Ideally, you want a combination where every upshift and downshift delivers a change in gearing that perfectly suits your legs. Riders that like to spin are likely to prefer small steps while those with more strength and a preference for a slower cadence will want bigger steps.

Thus, the former will enjoy compact rings and/or a straight block (which provides cogs in 1T increments) while bigger chainrings and/or larger increments in the cassette are likely to suit the latter. Bear in mind though, the suitability of the gearing is subject to your form and the terrain.

Final thoughts and summary

Ultimately, gearing is a personal choice and every rider should have the freedom to decide the matter for him/herself, but it will involve some experimentation. Fortunately, groupset manufacturers offer plenty of choices with 11-speed transmissions and compact/semi-compact/standard chainring combinations. The latter is further helped by new crank designs that allow compact, semi-compact, and standard chainring combinations to be interchanged.

It is futile judging the value of a particular chainring and cassette pairing on the basis of a single ratio. A 53T chainring will always offer a higher gear ratio than a compact 50T chainring but the two offer different rates of development, which ultimately dictates how the gearing evolves over the range of the cassette. At the same time, devoting some consideration to the overlap in gear ratios between the big and small chainrings may extend the versatility of the gearing.

What sort of gearing do you prefer? Compact or standard crank? Or perhaps a mid-compact? Why have you got the gearing setup you’ve currently got? Is it simply about the range of gears for you, or something more?

gearing is such a dick length measuring exercise. my impression is that low ratio gears and compacts are seen as uncool or hubbardly. yet i’ve been in so many races where i’ve been screaming out for lower ratio gears, and the riders who had the foresight to fit them just ride away up steep grades. i know the NRS guys can turn 39×25 up steep grades, but i’m thinking they don’t account for many of the bike sales of this ubiquitous ratio.

on the other hand, how many people can sprint in 53×11? not many, i’m thinking. oh, but you need it for downhills. BS. at that speed, you’ll go faster by stopping pedaling, and lying down on the top tube.

Anonymous Alpaca

I don’t often read comments on articles, but when I do I want them written by @disqus_bDUiSNPQWN:disqus. This was excellent.

jules

thanks. although possibly not as useful as the article itself :)

Sean

As a rule, I also steer clear of the comments. @jules does post some gems though.

jules

he’s an idiot!

Sean

me?

I’m sure CT thinks so.

Sean

Thinking about it….if I have to ask….I probably are.

jules

i was referring to myself Sean. some self-deprecating humour.

Anon

You forgot “You need 53 x 11” for Beach Road Strava chasing Jules.
I fitted a compact crank set 6 years ago, Since then never ever said, gee I wish I had a 53. Have said I wish I had a 12/28 at times rather than the 12/25 particularly at 3 Peaks

jules

mate i would happily take a 34×30 up the back of falls. don’t know how you can get up with a 25!

Anon bike shop whore

Working in a bike shop, I recently had a older gent tell me emphatically that he needed a 56 or 58T for the new top of the line road bike he was looking at (he wasn’t sure he could get chain rings in such large size to fit DA 9000). I expressed my surprise and asked why he needed such big gearing to which he responded absolutely straight faced- “Well when you get on the back of a fast bunch on Beach Rd, you can really pick up some speed you know”. Yeah mate… what ever… LOL

Simon

Good points Jules but I’d add that if you really want to be sneered at use a triple! I’ve gone from racing on a single gear as a juvenile way back where the strong kids could ride a maximum 81″ on a hilly course then to 52/42 like everyone did when it was the go in the 70s. (Look at pics of the pros stamping on their pedals pushing a 42 x 23 up mountains back then! ) Now in my dotage I happily use a compact for the big climbs, 50/34 12-30 and only ever use a 50/39 12-25 on Beach Road in calm conditions.

jules

as i understand it, the 42/23 of olden days was due primarily to manufacturing limitations – they didn’t have low enough BCDs for compact cranks and i’m unsure about rear cassettes but maybe they struggled with RD cage clearance? there’s little excuse these days.

I can sprint in a 55×11 no worries at all. I can sprint on my hands and knees also.

jules

i can sprint 55×11 too, it’s just that it looks like very hi fidelity slow motion :)

Jon

Damn right. I have a triple and love it.

Anthony Rochester

hang on, I think you have to draw a line somewhere…

pedr09

I got a compact on my most recent bike and have never missed the extra teeth. I’ve had mates ask how fast they need to go till I run out of gears but as you say Jules, by that time, we’re going down hill and I’m down on the top tube resting while they hammer away in futility.

Nick Squillari

Follow up with how Q-Rings/O-Symmetric come in to play?

Great piece though.

Jim

Do they come in compact ?
I need all the help I can get.

Dave Christenson

Running osymetric 52/42 and an 12-28 cassette gets me through pretty much any terrain but some steeper stuff in the 15-20% range is tough with the 42 chainring especially if it’s sustained for a long time. I guess a 42×28 would “feel” like a 39×26. I’m going to switch to 110 bcd next season and fit 52/38 osymetric rings to give me a bit more spin on the steep stuff to see how that works out.

Mark_Kelly

The article could be improved by incorporating St Sheldon’s concept of the gain ratio, which is the ratio of the speed of your tyre to the speed of your pedals: see http://sheldonbrown.com/gain.html.

On another note, I know this is a racing oriented site but you don’t even mention triples as a possibility.

Nick Liau

I’m happy for people to laugh at my 34×28 as I go flying past up hills.

Bob Dobbins

I was proud of my 34×28 until I tried to ride up the Santa Fe Ski Basin. Now they can laugh at my 34×32.

Raoul Luescher

Don’t forget crank length also plays a part in gearing, which is another debate in itself!!

Massimo

Great point, I’ve bucked the trend and at 183cm gone back to 170mm cranks.
I’ve found I have better cadence climbing and reduced the fatigue in my legs overall, to the point of having fresher legs the following day.
I have also found that the shorter crank length has not hindered my time trailing or criterium racing.

That’s interesting because over the last 5 years I’ve gone from 175mm to 172.5 and recently back to 175mm cranks again – all with 50/34 front and 12/28 back. The 2.5mm on each crank did make a difference. When I went to 172.5 it felt ugly in my quads – all jammed up, not fully accessing my optimal leverage, but I got used to it of course. 8 weeks ago I went back to 175mm cranks and the effect was amazing. So much better for me. Like a breathe of fresh air into my legs.

Sergio

For me 52X36 27/12 does the job any where.

Brick Descender

Alpine training with Jens was in the big 53 crank with the following gear ratio. 11-11-11-11-11-11-11-11-11-11-12. Note that they 12 tooth cog was a sign of weakness and meant that you were right for attacking!

ed

in 2003 i went across to switzerland & france. my lowest gear was 39-25 and i was unable to climb in the saddle over any of the big passes. i went back in 2007 with a 50/36 compact. my thoughts were that the pros push a 39-23 up the climbs, sometimes even a 25 so why do i think i can. it was heaps better and i was able to enjoy the climbs much more. when i got back i left the compact on and just changed around with the casettes – i mostly used a 11-23. everynow and then the 53/39 would go back on and it would normally take a week or two to get used to what gears to run on what hill. last year i upgraded to 11 speed and noted campag were doing a chainset with a 52/36 configuration. Its a good set up as it gives you plenty of options for all terrain.
in 2009 i had a knee injury and i found that the 53/39 was too hard on the knee up hills during recovery so i put the compact back on which didnt cause any problems.
apparenly carlos sastre used ot ride with a compact

Dave Christenson

Ed, you’re right that pros can push a 39×23 up climbs but a lot of them run compacts too…I just saw somewhere that even Kittel runs an 11-28 cassette at all times because at the high-end when he’s sprinting the gears are the same, he also uses a 53/39 which I was surprised by because he’s so big I’d thought he’d definitely be using a 54. Contador often uses compact crank and 11-32 cassette and I’m not sure but I would wager that Froome uses some of the osymetric 110 BCD chainrings to maintain that crazy cadence on the steep stuff. So the compact and climbing cassettes aren’t just used by us mortals ;)

velocite

Contador used 50/34 11/32 for the Angliru in the Vuelta a couple of years ago, was SRAM’s ‘WiFli’ derailleur. I bought that for the back of Falls and have never removed it. Smaller hills I go over on the big ring, and big ones I spin much faster and easier. I’m not a strong climber, but I notice not infrequently that towards the tops I spin past people who’ve stomped away from me lower down.

Johnny

For three peaks training about two weeks before the event I convinced (after years of trying) that he really didn’t need a regular crank. After that, it was the only time he was able to beat me going up hills.

eddy

42 is the answer

Robert Merkel

There’s some limited evidence to suggest that there might be an advantage to bigger front chainrings for sprinting. The IPHVA (recumbent speed merchants) ran an article back in 2001 which indicated that cogs bigger than 12 teeth had slightly higher mechanical efficiency than 12-tooth (and presumably 11-tooth) cogs.

The question is whether this is relevant at sprinting wattages – they tested at around 200 watts, when a typical sprint is going to average at least 700 watts and peak at over 1000.

i’d imagine the reason for those losses would be the sharper ‘drop off’ of lower-count cog teeth as they disengage with the chain being pulled towards the chain ring. i don’t see that improving with power output.. tony martin runs bigger teeth on his TT bike too, but i read that was more to do with maintaining a straight chainline.

Dave

Could well be.

It might also be to do with the sharp bend in the chain. Cancellara runs larger jockey wheels on his derailleurs for that reason.

Sean Doyle

Generally in industry they use 17t sprockets or bigger. You do actually gain efficiency as the sprocket gets bigger as you get a smoother path of the sprocket for each pivot. If i could get away with a 14t smallest sprocket, as a compromise, I would run that but the chainring becomes obscenely oversized to maintain ratios.

Notso Swift

52/36 is where it is at.

Priestie

I love big gears, they suit me, those that ride with me know I average a very low cadence but can push big gears. I love 53×11 on the flats, it is my favourite gearing.

However after fitting 53/39 with a power meter, I now miss my compact, 53/39 only gives me ‘real’ satisfaction when its time to dig deep, for me 53/39 can really tire the legs quicker over a ride. Compacts are versatile, suits everyday riding and can keep the legs fresh. With a 11-28T cassette on both the 53/39 and compacts, I found smoother leg work and transition in gears with the compacts.

If it wasn’t for a difference in BCD, I’d go back to compacts, and use a mid compact for those top end speeds to help develop my leg speed.

A series to this piece may also be finding the optimal power vs gear selection. Again, I’m a gear grinder but after 6 months of using compacts again, it retaught my pedal stroke and I was able to push out greater watts for longer with fresher legs, a higher cadence, and a pedal stroke which rotated more correctly with both a down and upstroke, compared with larger 53×11 I push down more so than up.

Dave

The new Campagnolo groupsets have the same BCD for all chain ring sizes, so in theory you might be able to mix and match chain rings.

It would be interesting to see how the shifting works with spreading the ratios further apart to a 52/34, 53/36 or even a 53/34 combination. If it worked, you’d lose a few mid-range ratios but gain the big advantage of having climbing gears and sprinting gears both on the bike at once.

echidna_sg

totally agree, not to mention the ability to simply carry a couple of extra chainrings and a chain for swapping around from day to day as the parcourse demands.

velocite

There are limitations on mixing and matching. My SRAM 50 big ring carries the note ‘for use only with 34 little ring’. And if you fit the little ring incorrectly relative to the big ring shifting up is stuffed: the chain will end up sitting on top of the teeth. The ramps on the big ring are designed for an integral number of links to be doing the jump up, to put it rather clumsily.

As far as a 54/34 is concerned, so long as your rear derailleur can cope with the range I think it’s all win: you get a greater range and all you lose is overlap – a good thing!

Dave

Yep.

There’s a very good reason that I wrote phrases like “in theory you might be able to”, “it would be interesting” and “if it worked.”

Unfortunately I can’t afford to buy up a whole lot of Campy kit to try it out!

velocite

Although I had read the label, I only discovered the reason for it after I inadvertently fitted a replacement small ring incorrectly. It hadn’t occurred to me that it would matter how it was oriented, and I didn’t notice the little index mark, which I later discovered was meant to be aligned with the crank. Shifting non-performance drove me crazy till I discovered the reason. Does the same in fact apply to Shimano and Campy?

Harry Sacks

I have only been riding for 18 months now. My bike at home is 53/39 with an 11-25, and it is all I had ever known until recently. I do really feel fire in my legs after big climbs as I struggle to keep a rhythm or get a decent cadence going in 39-25. I came to France to watch the Tour and ride a rental bike up some of the famous climbs here in France. It was fitted with 50/34 and a 12-28. I absolutely loved spinning up the hills, and really loved the smoother increments on the flats. My legs definitely thanked me during, and at the end of each ride. I am definitely more suited to short sprints, bombing hills, or pushing along the flats than I am suited to climbing anything over 1%, but I am going to fit compacts with possibly an 11-28 when I return home.

I did miss sitting in 53-11 when punching down a few hills, but really I am in this situation maybe .5% of the time I spend riding, so I have no problem giving that ratio up for the remainder of my rides. And as jules says, I probably would be better off putting my ruler away and just lying down for the descent.

James C

I ride with 52/38 up front and a 14-25 10 speed cassette, perfect for junior road and circuit racing

This is my absolute favourite time waster when used in combination with online shopping for bike parts

Memphis

Thanks for that dude

Jammy

I haven’t heard meters of development before. In motorsport often it’s called rollout (as in distance of roll you get for each turn of the crankshaft). What I don’t think many people realise is that the difference between a 54t and a 50t is really only one tooth on the cassette. It is that simple really. I’m not being a ‘compact apologist’ either. Anyone that sniggers or laughs at compacts probably hasn’t really thought about it, is more concerned with looking PRO than being nice, and is probably a bit uncool to ride with anyway…
I really like the analysis of the differences between cassette gears between std and compact. I’d never thought of it before, but compact does seem to provide tighter gaps between gears on the cassette, making it easier for me to find an ideal cadence on slight inclines or headwinds. I run 50/34 and 12-28 because that is what came on my bike. I get smashed by stronger riders on the group rides, and struggle to push even the 28 on 12% a couple times each week, but I also have had knee issues running and pushing heavy gears can exacerbate that, so it is what I am stuck with!
I also find I can ride a lot in just the big ring, not needing to change so much on the front derailleur saves some admin and concentration. Particularly on long shallow inclines or steep rollers. I know I am finding form (all done in a knee safe manner mind you) when I’m still in the 50 on the first couple turns of a few 7%ers around here.
I get faster drivetrain wear I guess from cross chaining, but I’ve never understood people getting upset about drivetrain maintenance and having to change a $40 chain earlier on the one hand, while riding on $2k carbon rims on the other..
Great article, keep it coming!

Dave

Rollout is what it’s usually called in cycling as well.

As for “one tooth on the cassette” – entirely correct! 54/12=4.50, 50/11=4.54

velocite

Correct between 11 and 12, but not 27 and 28. That of course is why the gaps between the bigger cogs are 3 or 2 teeth while the smallest cogs are a tooth apart.

Boris

Wouldn’t the pro teams change gearing often based on terrain, wind, form, etc? On a flat stage why you’d surely want 11-12-13-14 etc, whereas on a mountain stage 11-13-15 at the bottom end to give you more up the range?

Nugraha Nandiwardhana

I run 52/39 and 12-25 as I kept on maxing out the gears when I used to run a 50/34 crank. On flats I’m more comfortable pushing big gears (52/14 or 52/13 at 90ish RPM) than spinning at 50/12, and when it comes to flyovers (which I dearly love), I’d usually shift to 15 or 17 and bomb my way up past the bunch.

Periscope

What a legend

flrider

living in Florida a 53×11 is fine on the pancake roads and 30mph group rides

Richard

When I raced back in the days of six and seven speeds I rode 12 straight block with a 52/39. Colorado has some hills. The 39/18, or 21 if I skipped some teeth at the bigger cog end of the block was fine back then for hills.
Now I’m older and ride a triple on the hills here with ten choices of cogs out back.
I rode RAGBRAI for a five days and never got out of the middle ring. I spent most of my time where I usually do, in the middle of the cogs and the middle ring.
I’ve been in the big ring on this bike maybe a half dozen times in the 5,000 miles I’ve ridden it. Old knees don’t like crushing gears, they prefer spinning.

Craig

Switched from a standard to a compact after swearing my way up the Falls Creek back road at 7kph in my first 3 Peaks. Most of the year I run a 52/36 with a 12-27 and switch when I’m going longer and steeper to a 50/34. Happy times :)

Daryl Brice

I run a compact crank with a 12-32 cassette. That takes me anywhere I need to go. I do not race but do go for Strava KOM’s

Alex Read

All quite well put. I personally love a standard at the front because it let’s you get up to speed on the flats (particularly on a TT bike) so damned quick. Could be that I went from a 105 compact to a SRAM Red standard, though, which is just a damned beautiful thing, The other compact on which I’ve ridden was a Tiagra, which felt particularly weak.
New roadie came with a 53/39 and 12-25. Screw that noise. Nobody outside of the pro ranks should bother with that kind of combo. I don’t care who you are, someday you are going to be a few hills from home and hunger flatting with no team car to hop in. Just ordered a 11-28. Nice big range can surely handle anything. If with training I can’t do 3-Peaks in a 39/28, I’ve got bigger issues than gearing.

Bob Dobbins

My two cents…assume you know your “long stretch” training speed. By that, I mean how fast you would ride on a relatively flat course over a course of 20 or 25 minutes when you are training for your big outing. For me, it is about 18mph (no, I am not pro but I can hold that pace for a long time). Now figure out the gear ratio required for that speed at a cadence of 100 rpm. That gear should be your big ring up front and the middle ring in the back. Everything else will fall in place. PS Sheldon Brown has a nice gear ratio calculator that will help you figure this easily

Dave2020

A jump of 14 or more teeth on the chainrings is a compromise that’s not fit for purpose. Over forty years ago I raced with a triple (39, 46, 53), a close-ratio 6-speed and bar-end levers. Never had to make a double change. All the guys riding the then-standard 42-52 with down-tube levers were at a distinct disadvantage.

Narrow chains are bad engineering, designed to wear out in a year. I showed Campagnolo how to make an 11-speed (standard chain width) twenty years ago, as derailleurs went up to 8-speed plus. Sensible (conventional) design should have settled on 3×8, but somehow a stigma became attached to the triple. How dumb can you be?

Froome showed on Mont Ventoux last year that there are times when the state-of-the-art double can be a right pain – when the chain is scraping on a small ring/small cog combo, but changing up to the big ring simply isn’t an option.

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